Various implantable drug delivery devices are known in the art which can be programmed to deliver a drug to a body site for infusion at flow rates and times dictated by a stored drug delivery profile. Such delivery devices typically include a refillable reservoir for storing a fluid drug and a controllable fluid transfer device (e.g., a pump or valve) for transferring fluid from the reservoir to a catheter for delivery to the body site. The drug delivery profile comprises a data set specifying a schedule of flow rates for a periodic cycle, or period, of a certain duration. For example, the duration of a period can be twelve hours, twenty four hours, or one week, etc. The particular profile used to control drug delivery is typically specified by the patient's clinician and depends upon several factors including the particular drug formulation being delivered, the patient's condition, the therapy being administered, etc.
The delivery profile is typically stored in the medical device at the time of implanting and can thereafter be modified by a clinician (using an external controller or programmer) when the patient periodically visits for a refill/checkup, e.g., once per month.
In the course of certain drug therapies, it may be desirable to increase or reduce the drug dosage delivered to the patient. For example, in some situations, it may be helpful to reduce or terminate drug administration for a limited period in order to increase the patient's sensitivity to the drug. In still other situations, it may be desirable to terminate delivery of a drug as an initial step in preparation for changing the drug formulation.
For illustrative purposes, in situations where a therapeutic decision has been made to reduce or eliminate delivery of a certain drug, it is generally desirable to reduce the drug dosage gradually. This gradual reduction, which is sometimes referred to as a detoxification procedure, is relatively easy to administer if the patient is available to the clinician on a frequent basis, e.g., daily. However, in the use of implanted drug delivery devices, patients typically visit their clinicians infrequently, e.g., once per month, and it has therefore been inconvenient and impractical to administer a drug modification program. The present invention is directed to an implantable drug delivery apparatus and method of operation which facilitates the automatic gradual modification, e.g., reduction of drug delivery over an extended interval, e.g., many days.